PHILADELPHIA — House Speaker Paul D. Ryan expects President Donald Trump to submit a roughly $15 billion supplemental appropriations request to pay for his border wall, but neither Ryan nor Senate Majority Leader Mitch McConnell would detail whether the cost will be offset by spending cuts or paid for with deficit spending, nor whether Mexico would ultimately pay for it, as Trump promised repeatedly during the 2016 campaign.

“As far as the offset, we’re going to wait for the administration and see what their supplemental looks like,” Ryan said at a media availability with McConnell on Thursday at the GOP’s issues retreat here.

While Ryan said the wall along the southern border would cost “roughly $15 billion,” McConnell provided an initial cost range of $12 billion to $15 billion. Estimates from outside the Republican Party peg the cost as high as $25 billion.

The president and his team pivoted recently to stating that Mexico would reimburse the United States for the cost of the wall after U.S. taxpayer money first pays for it. Mexican officials have laughed this idea off consistently.

The issue came to a head this week again after Trump signed an executive order on Wednesday designed to expedite construction of the wall. Mexican President Enrique Pena Nieto followed with a statement saying that he “regrets and rejects” the proposed wall and there was no way his country was paying for it.

Trump retaliated Thursday morning in a tweet that threatened to cancel his scheduled meeting next week with Pena Nieto. Hours later, Pena Nieto said he told the White House he was canceling the meeting.

Pressed on the kerfuffle, McConnell declined to weigh in on that disagreement.

“We intend to address the wall issue ourselves, and the president can deal with his relationships with other countries,” the Kentucky Republican said. Mexico is the United States’ third-largest trading partner among countries worldwide, behind Canada and China.

While the top two congressional Republicans would not commit to how to pay for the wall, Ryan said he and McConnell are still fiscal conservatives.

GOP plans to overhaul the health care system and create jobs are two things that will “dramatically” help improve the budget situation, the speaker said, when asked if the GOP was committed to ensuring that legislation enacted under their agenda would not add to the deficit.

Since there is no accompanying legislation that the Congressional Budget Office or any other arbiter can score, the Wisconsin Republican’s claim cannot be verified.

“If we’re going to be spending on things like infrastructure, we’re going to find the fiscal space to pay for it in our spring budget,” Ryan said.

New York Rep. Chris Collins, an early Trump supporter, said he’s going to leave the details to Trump. “The president said he’s going to get reimbursed one way or the other. We accept that. … I’ll trust him on that without knowing any details,” he said on Wednesday.